AP Biology Unit 2: Cell Structure and Function Vocabulary

Comprehensive vocabulary flashcards covering key terms and concepts from AP Biology Unit 2: Cell Structure and Function.

Cell Theory

A foundational biological principle stating that all organisms are composed of cells, cells are the structural and functional units of life, and all cells arise from pre-existing cells.

Prokaryotes

Single-celled organisms belonging to the domains Bacteria and Archaea that lack a nucleus and membrane-bound organelles and reproduce by binary fission.

Eukaryotes

Organisms belonging to the domain Eukaryota (including plants, animals, protists, and fungi) whose cells contain a membrane-bound nucleus, complex organelles, and linear chromosomes.

Archaea

Single-celled prokaryotes that lack peptidoglycan in their cell walls, possess unique ether-linked membrane lipids, and often inhabit extreme environments such as high salt or high temperature.

Endosymbiotic Theory

The evolutionary theory stating that mitochondria and chloroplasts originated when early eukaryotic host cells engulfed free-living aerobic or photosynthetic prokaryotes in a mutually beneficial relationship.

Cytosol

The fluid portion of the cytoplasm, consisting primarily of water, dissolved ions, and proteins, excluding membrane-bound organelles.

Nucleus

A double-membrane organelle in eukaryotic cells that houses genomic DNA, serves as the site of transcription, and regulates cellular activities.

Nucleolus

A dense region within the eukaryotic nucleus responsible for synthesizing ribosomal RNA ($rRNA$) and assembling ribosomal subunits.

Ribosome

A non-membrane-bound subcellular structure composed of ribosomal RNA ($rRNA$) and proteins that carries out protein synthesis during translation.

Endomembrane System

A group of interconnected membrane-bound organelles—including the nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, vesicles, and plasma membrane—that work together to synthesize, modify, package, and transport proteins and lipids.

Rough Endoplasmic Reticulum (Rough ER)

A network of folded membranes studded with ribosomes on its outer surface that synthesizes and folds proteins destined for membranes, lysosomes, or secretion.

Smooth Endoplasmic Reticulum (Smooth ER)

A network of tubular membranes lacking ribosomes that synthesizes lipids (such as phospholipids and steroids) and detoxifies drugs and metabolic waste products.

Golgi Apparatus

A series of flattened membrane-bound sacs (cisternae) that chemically modifies, sorts, and packages newly synthesized cellular products into vesicles for trafficking.

Cis Golgi

The receiving entry face of the Golgi apparatus located nearest the endoplasmic reticulum that accepts transport vesicles containing newly synthesized proteins and lipids.

Trans Golgi

The exit face of the Golgi apparatus facing the plasma membrane that sorts and buds off processed proteins and lipids into vesicles bound for their final destinations.

Lysosome

A specialized membrane-bound vesicle containing hydrolytic enzymes in an acidic environment used for intracellular digestion, organelle recycling, and programmed cell death (apoptosis).

Peroxisome

A membrane-bound organelle containing oxidative enzymes (such as oxidases and catalase) that break down fatty acids and convert toxic hydrogen peroxide ($H_2O_2$) into water and oxygen.

Mitochondrion

A double-membrane organelle with an inner folded membrane (cristae) and fluid matrix that produces ATP through aerobic respiration (Krebs cycle and electron transport chain).

Cristae

Infoldings of the inner mitochondrial membrane that significantly increase the available surface area for electron transport chain proteins and ATP synthesis.

Chloroplast

A double-membrane organelle found in plants and algae containing thylakoids stacked in grana within a fluid stroma, serving as the site of photosynthesis.

Thylakoid

A flattened, membrane-bound sac inside a chloroplast containing chlorophyll and photosynthetic pigments where light-dependent reactions take place.

Stroma

The fluid-filled space surrounding the thylakoid membranes inside a chloroplast where the Calvin cycle (carbon fixation) occurs.

Central Vacuole

A large membrane-bound organelle in plant cells that stores water and solutes while maintaining turgor pressure against the cell wall.

Turgor Pressure

The outward hydrostatic force exerted by water inside the central vacuole against the cell wall of a plant cell, giving it structural rigidity.

Contractile Vacuole

A specialized organelle in freshwater protists that actively collects and expels excess water to prevent osmotic lysis in hypotonic environments.

Cell Wall

A rigid, nonliving outer layer adjacent to the plasma membrane present in plants (cellulose), fungi (chitin), bacteria (peptidoglycan), and archaea that provides structural shape and prevents lysis.

Cytoskeleton

A dynamic network of protein filaments—microfilaments, intermediate filaments, and microtubules—that provides structural support, maintains cell shape, and aids in intracellular transport and cell movement.

Microfilaments

Cytoskeletal fibers made of two intertwined chains of actin monomers (approx. $7\,nm$ in diameter) that support cell shape and facilitate cell movement.

Intermediate Filaments

Rope-like cytoskeletal proteins such as keratin (approx. $8\text{--}12\,nm$ in diameter) that reinforce nuclear and cell membranes and anchor organelles.

Microtubules

Hollow cylindrical cytoskeletal structures composed of tubulin proteins (approx. $25\,nm$ in diameter) that form tracks for motor proteins, construct spindle fibers, and structure cilia and flagella.

Surface Area-to-Volume Ratio ($SA:V$ Ratio)

The relationship between a cell's outer membrane surface area and its internal volume; higher ratios in smaller cells facilitate more efficient diffusion and nutrient/waste exchange.

Fluid Mosaic Model

A structural model depicting the cell membrane as a flexible phospholipid bilayer embedded with a mosaic of mobile proteins, cholesterol, glycoproteins, and glycolipids.

Amphipathic

Describing a molecule that contains both hydrophilic (polar) and hydrophobic (nonpolar) regions, such as a phospholipid.

Cholesterol

A steroid lipid embedded within the phospholipid bilayer of animal cells that stabilizes membrane fluidity across temperature extremes.

Homeoviscous Adaptation

The cellular process of altering membrane phospholipid composition (such as increasing unsaturated fatty acids) in response to cold temperatures to maintain optimal fluidity.

Integral Protein

A membrane protein permanently embedded within or spanning across the hydrophobic core of the phospholipid bilayer.

Peripheral Protein

A protein loosely attached to the inner or outer surface of the plasma membrane or bound to integral proteins.

Glycoprotein

A membrane protein covalently bonded to carbohydrate chains that plays key roles in cell recognition, cell adhesion, and immune signaling.

Glycolipid

A membrane lipid covalently attached to carbohydrate chains that aids in cell recognition, communication, and formation of the glycocalyx.

Selective Permeability

The property of biological membranes that allows small nonpolar molecules ($O_2$, $CO_2$, $N_2$) to pass freely while restricting ions and large polar molecules.

Passive Transport

The net movement of solutes across a membrane down their concentration gradient (from high to low concentration) without direct input of metabolic energy ($ATP$).

Active Transport

The movement of solutes across a membrane against their concentration gradient (from low to high concentration) requiring energy ($ATP$) and transport proteins.

Simple Diffusion

Unassisted passive movement of small, nonpolar molecules directly across the hydrophobic core of the phospholipid bilayer from high to low concentration.

Facilitated Diffusion

Protein-mediated passive transport of polar molecules or ions across a membrane down their concentration gradient using specific channel or carrier proteins.

Aquaporins

Specialized transmembrane channel proteins that facilitate the rapid passive movement of large quantities of water molecules across plasma membranes.

Osmosis

The net movement of water molecules across a semipermeable membrane from a region of low solute concentration (high water potential) to high solute concentration (low water potential).

Hypotonic Solution

A solution with a lower solute concentration relative to the cell's cytoplasm, causing water to enter the cell and leading to cell swelling, lysis, or turgidity.

Hypertonic Solution

A solution with a higher solute concentration relative to the cell's cytoplasm, causing water to leave the cell and leading to cell shrinkage, crenation, or plasmolysis.

Isotonic Solution

A solution with an equal solute concentration relative to the cell's cytoplasm, resulting in no net water movement across the membrane.

Plasmolysis

The shrinking of the cell membrane away from the rigid cell wall in plants, fungi, or bacteria when placed in a hypertonic environment.

Water Potential ($\psi$)

A quantitative measure of the tendency of water to move from one area to another, calculated as the sum of pressure potential ($\psi_P$) and solute potential ($\psi_S$).

Solute Potential ($\psi_S$)

The component of water potential that decreases with increased solute concentration, calculated by the formula $\psi_S = -iCRT$.

Sodium-Potassium Pump ($Na^+/K^+$ Pump)

An electrogenic transport protein that uses ATP to actively pump $3\,Na^+$ ions out of animal cells and $2\,K^+$ ions in, maintaining the resting membrane potential.

Membrane Potential

The electrical voltage difference across a plasma membrane generated by an unequal distribution of ions between the cytosol and extracellular fluid.

Cotransport

A active transport process where the favorable movement of one solute down its concentration gradient is coupled with the unfavorable transport of another solute against its gradient.

Symport

A cotransport protein mechanism that transports two different substances across a membrane simultaneously in the same direction.

Antiport

A cotransport protein mechanism that transports two different substances across a membrane in opposite directions.

Endocytosis

An energy-requiring bulk transport process where the cell membrane invaginates to form vesicles that engulf extracellular fluid or solid particles into the cell.

Exocytosis

An energy-requiring bulk transport process where intracellular secretory vesicles fuse with the plasma membrane to release materials outside the cell.

Phagocytosis

A form of endocytosis ('cell eating') in which a cell surrounds and engulfs large solid particles or microorganisms into a vacuole or phagosome.

Pinocytosis

A form of endocytosis ('cell drinking') in which a cell non-specifically takes in droplets of extracellular fluid containing dissolved solutes.

Receptor-Mediated Endocytosis

A highly selective form of endocytosis where target molecules (ligands) bind to specific cell-surface receptors, triggering vesicle formation in coated pits.

Cell Compartmentalization

The organization of eukaryotic cells into distinct membrane-bound sub-environments, allowing specialized biochemical processes to occur simultaneously without interference.